Table 1 Thermodynamic parameters of bortezomib binding from ITC and fitting to the MWC model.

KR and KT refer to the bortezomib association constants for the relaxed and tense state. ΔHR, ΔHT, and ΔHγ refer to the binding enthalpy of the R state, T state, and conformational enthalpy between R and T conformations. γ is the equilibrium constant between R and T conformations in the absence of the ligand. N is the fraction of active or binding-competent protein. Relative errors in equilibrium constants are 30%. Absolute error in enthalpies is 0.3 kcal/mol.

T (°C)NKR
(M−1)
ΔHR
(kcal/mol)
KT
(M−1)
ΔHT
(kcal/mol)
γΔHγ
(kcal/mol)
25°C0.974.5 × 104−0.5No apparent cooperativity
35°C0.978.0 × 104−0.92.8 × 104−0.13.3−0.3
45°C1.006.5 × 104−1.52.5 × 104−0.33.2−0.2